----- Original Message -----
From: "Christopher Dore" <[log in to unmask]>
To: "'Matthew Sterner'" <[log in to unmask]>
Sent: Monday, October 20, 2003 9:43 AM
Subject: Digital Photogrammetry


We (Statistical Research) routinely use digital photography as a
photogrammetric tool for documenting various excavation (and other)
features.  We use platforms that include terrestrial, ladder, cherry picker,
balloon, and kite.  We use all three major types of photogrammetry:  simple
(2-D correction), convergent, and stereo).  Simple photogrammetry yields
accuracies better than the measured drawings done by our field techs and
saves us a lot of dollars in mapping, drafting, and getting illustrations
into reports.  Convergent photogrammetry is used for higher-end projects
when we really need the 3-D coordinates or when the stakes are higher
(expert testimony for ARPA cases, for example).  Under practical use
conditions, convergent photogrammetry give us accuracies at about 1 part per
2,000.  We use stereo photogrammetry for when extreme accuracy is needed,
when we need digital elevation models and secondary data sets (e.g. topo
lines), or when we need ortho photos.

Digital photography is technically better for photogrammetry because there
is no film distortion.  You just need to ensure that the resolution (in real
ground units) is sufficient for your application.  Unfortunately, most
digital cameras have zoom lenses which generally can't be used for
convergent or stereo photogrammetry (although sometimes you can get away
with it if you are zoomed all the way in or out).  Rollei now makes digital
metric cameras (metric cameras are those designed for photogrammetry).  For
software, we use TNTmips for simple and stereo photogrammetry and use
PhotoModeler for convergent photogrammetry.

Anyone can easily be trained to take photogrammetrically suitable
photographs using off-the-shelf cameras, at least for the simple and
convergent techniques.  We offer a 1/2 day training workshop called
"Introduction to Archaeological Field Photogrammetry" and will next give
this workshop on 8 November in Tucson.  This workshop gives you sufficient
training to take field photographs that can be used for photogrammetry.
While this 8 November workshop is full, you can email me off list to be
notified about upcoming workshops or presenting a custom workshop at your
office/university/field school.

Christopher


===================
Christopher D. Dore, Ph.D., RPA
Director, Department of Cartography & Geospatial Technologies
(President of the American Cultural Resources Association)

Statistical Research, Inc.
P.O. Box 31865
Tucson, AZ   85751-1865

1.520.721.4309 (voice)
1.520.298.7044 (facsimile)
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www.sricrm.com